Add push notification support for Android and iOS

- Integrated Firebase Cloud Messaging (FCM) for Android
- Integrated Apple Push Notification Service (APNs) for iOS
- Created shared notification models and API client
- Added device registration and token management
- Added notification permission handling for Android
- Created PushNotificationManager for iOS with AppDelegate
- Added placeholder google-services.json (needs to be replaced with actual config)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

composeApp/google-services.json

@@ -0,0 +1,29 @@
+{
+  "project_info": {
+    "project_number": "YOUR_PROJECT_NUMBER",
+    "project_id": "your-project-id",
+    "storage_bucket": "your-project-id.appspot.com"
+  },
+  "client": [
+    {
+      "client_info": {
+        "mobilesdk_app_id": "1:YOUR_PROJECT_NUMBER:android:YOUR_APP_ID",
+        "android_client_info": {
+          "package_name": "com.example.mycrib"
+        }
+      },
+      "oauth_client": [],
+      "api_key": [
+        {
+          "current_key": "YOUR_API_KEY"
+        }
+      ],
+      "services": {
+        "appinvite_service": {
+          "other_platform_oauth_client": []
+        }
+      }
+    }
+  ],
+  "configuration_version": "1"
+}